<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script>
      window.onload = function () {
        // 高阶函数，函数可以作为参数传递
        function fn(a, b, callback) {
          console.log(a + b);
          callback && callback();
        }
        fn(1, 2, function () {
          console.log("最后调用");
        });
      };
    </script>
  </head>
  <body></body>
</html>
